COATED PIPES AND METHODS OF MAKING THEM

Abstract: A method of coating a pipe comprising the steps of: (i) rotating a pipe to be coated about its longitudinal axis, and (ii) applying a coating to the pipe from a dispensing head movable parallel to the axis of rotation of the pipe.

Description: COATED PIPES AND METHODS OF MAKING THEM This invention relates to methods of pipe coating, pipes made by the methods, and apparatus for making the pipes. The invention provides for providing insulating or protective coatings on pipes by pouring or otherwise applying material onto a rotating pipe. According to the invention there is provided a method of coating a pipe comprising the steps of: i rotating a pipe to be coated about its longitudinal axis, and ii applying a coating to the pipe from a dispensing head movable relative to the pipe parallel to its axis of rotation. In some embodiments of the invention the heads are fixed and the bed traverses. An embodiment of the invention will be illustrated by reference to Figure 1. The apparatus comprises a bed 1 provided with chucks 2. The pipe 3 to be coated is mounted in the chucks 2 and caused to rotate. To obtain very high quality product the rate of rotation should be carefully controlled by first controller 3a. Coating is dispensed from head 4. Head 4 i≤ typically air or electrically driven and may traverse along guides. Where the coating is the reaction produce of two components they may be supplied by separate feeds 5,6 to the head where they mix and react. Alternatively or additionally they may be mixed prior to supply to the head or they may react on the pipe. Head 4 is arranged to move parallel to the axis of the pipe 3. The rate of traverse and rate of dispersing are controlled by second controller 7 which may be microprocessor based. Typically layers up to about 20-25mm can be routinely dispensed. Further layers can be applied from further heads 4a,4b traversing behind head 4. Multiple layers can readily be applied in this manner with extremely good inter-layer adhesion being achieved. The further heads may apply the same or different material to the pipe. Four layers can be routinely applied in a single pass. The further heads need not wait for the first head to complete its traverse before applying their coating. Where the heads are fixed and the bed traverses it then the heads generally make a single pass. ' One or more heads in some embodiments make multiple traverses. The coating is allowed to cure to a handleable condition and then removed from the apparatus. The coated pipe may have a central coated portion and bare ends. The ends are thus free of the poured coating ready for joining, for example using currently available field joint systems or as described in copending UK application number 93 24 147.9. A wide range of coatings can be applied. For example a conventional steel pipe may be coated with an anticorrosion coating of fusion bonded epoxy (FBE) or rubber. These layers may be applied in conventional manner for example spraying or extrusion. Application of epoxy primer in liquid form is a preferred pretreatmen . Syntactic polyurethane (PU) can then be applied. Multiple layers of total thickness up to 60mm giving a U-value of less than 2.5W ** _ 2κ~- * - can readily be applied. This system has been tested on pipes up to (16 inch) 0.4m diameter to give a very satisfactory product substantially free of voids and consistent throughout the thickness. Table 1 compares the properties of a syntactic PU applied in accordance with the invention with product moulded in- a traditional way. Table 1 Invention Control Density 700-760kgm ~3 77n0n0-_.77κ6n0ki-rg,m m - ' 3 Hardness 80 Shore A 90 Shore A Tensile Strength 5.5 MPa 6.5 MPa Compressive Modulus 1.5 MPa 2.0 MPa Elongation at Break 100% 60% Abrasion Resistance 1300mm J 1300mm--' Thus i * c will be noted that the properties of the produce of the invention are very satisfactory with notably good elongation at breaking. Additionally traditional coating of thick layer syntactic foam on large diameter pipe can lead to a poor quality, low density product due to thermal expansion of the polymer spheres in what is known as a "free rise situation". The process of the invention has a marked decrease in the probability of this problem. The process of the invention is also cost effective. Typically the process of the invention is 5- 15% cheaper than traditional methods. Savings occur in a number of areas. Losses in mould-filling amount to about 5-20% in the prior art processes. This is substantially eliminated in the invention. Typically to ensure the prior art processes provide product meeting the contracted specification the pipe is provided with about 2mm "extra" coating. Because the process of the invention is so controllable this excess can be reduced saving a further 4-10% of coating material. Labour costs are also reduced. The labour required to apply and cure the coating is reduced by 75%. Since there is no mould the labour required for demoulding and cleaning the mould is eliminated. A labour cost reduction of 10-20% may be anticipated. Overall a cost reduction of 5-15% can typically be achieved. Although the equipment is expensive, overall the process is not capital intensive since a wide range of product can be produced using the plant. Conventional moulded foams tends to have an axial and/or radial density gradient due to differential rising of the blown foam. The invention substantially reduces this gradient. Possible • coatings include low density rigid PU foam. This is very suitable for use in shallow waters land approaches and on-shore installations. It may be applied over FBE and can have a density of 80-200Kgm -* ^. At a thickness of 75mm the product has a U-value of less than 0.5 Wm~ 2 k~ 1 . Urethane-modified polyisocyanurate foams (PIR) can be applied in bulk densities typically 80-450 kg -^ (i.e. suitable for depths up to 250m) . They may be applied as thermal insulation on top of primers and/or anticorrosion coatings. PIR is thermally stable and may be used at 140°C in contrast with PU foams which have a maximum service temperature of no greater than 110°C. Polyurea elastomer can be applied. This material is stable at very high temperatures (in excess of 160°C). The polyurea may be applied to steel or a primed surface as an anticorrosion layer. If desired further layers for example of foam insulant may be applied over the polyurea. High Density Rigid Polyurethane Foam can also be applied using the invention typically to pipes having FBΞ and or rubber base coats. The system has been satisfactorily tried on (16 inch) 0.4m diameter pipe with coating up to 50mm thick. Typical bulk densities range from 250kgm~ 3 (suitable for use at 150m at 75°C) to 450kgm -3 (suitable for use at 250m at the same temperature) . Table 2 compares the product of the invention with prior art products. Table 2 Invention Control Density 450kgm ~3 450kgm -3 Tensile Strength 5.0 MPa Elongation at Break 5% 1-3% Co pressive Modulus 15 MPa 10-12 MPa It may be used as a stand alone coating or may be overcoated for example with solid PU elastomer water barrier coatings. Typical coating thickness 3mm or greater. The following coatings may be applied alone or in combination with others. A high mechanical strength coating may be adopted having say a hardness of 95 Shore A tensile strength of 40 MPa elonσation at break of 350% and abrasion resistance 100mm- 3 . A coal tar/urethane coating typically applied in layers of 3mm or greater may be applied and may for example protect FBE from rock dumping and minor impacts. Typical properties are hardness of 85 Shore A tensile strength of 20 MPa, elongation at break of 300% and abrasion resistance 350mm 3 . Solid PU or other nonfoamed materials may be applied for example as an outer jacket over foamed coatings. This fully encapsulates the foam and substantially reduces water penetration and provides impact protection. Solid i.e. nonfoamed PU may also be applied as an impact crack arrestor for example under a syntactic PU or PU foam/solid PUjacket. Solid PU may also be applied to primed steel or FBE. Table 3 compares the properties of solid PU applied in accordance with the invention with that moulded according to prior art processes. Table 3 Invention Control Hardness 90 Shore A 90 Shore A Tensile Strength 15 MPa 15 MPa Elongation at break 250% 300% Abrasion resistance 110mm 3 110mm 3 Other coatings include pressure resistant syntactic PU usable to 450m at 110°C and processible through standard PU equipment and PU elastomeric weight coatings for minor adjustments of submerged weight. Thin layers of say up to 5mm may be applied and can be laid from a reel ship. The process of the invention is desirable on environmental grounds due to the reduction in spillage and wastage and exposure of personnel to coating materials. The invention is also very flexible as short joints, interrupted coatings, taper or stepped transition joints can be produced. Since there is no mould changes in thermal design can be readily accommodated by changing the commands issued to the heads.

Claims: CLAIMS: 1. A method of coating a pipe comprising the steps of: i rotating a pipe to be coated about its longitudinal axis, and ii applying a coating to the pipe from a dispensing head movable parallel to the axis of rotation of the pipe. 2. A method of coating a pipe as claimed in claim 1 wherein the coating is a polyisocvanurate, a polvurethane or urethane-modified polyisocyanurate. 3. A method as claimed in claim 1 or claim 2 wherein the coating is a foam optionally having a bulk density in the range 80-450 kgm -3 . 4. A method as claimed in any one of the preceding claims wherein the pipe is a steel pipe having a coating of epoxy primer or fusion bonded epoxy resin. 5. A method as claimed in any one of the preceding claims wherein a second coating layer is applied to the pipe from a dispensing head movable parallel to the axis of rotation of the pipe. 6. A method of coating as claimed in claim 5 wherein the second coating layer is of the same material as the first layer. 7. A method as claimed in any one of the preceding claims wherein the pipe ends are left uncoated. 8. A method as claimed in any one of the preceding claims wherein the supply of coating to the head is controlled by a controller so as to produce a tapered coating or and interrupted coating. 9. A method as claimed in any one of the preceding claims wherein the pipe coating is 5 to 75 mm thick preferably 25 to 75 mm thick. 10. A pipe coated in accordance with a method as claimed in anv one of claims 1 to 9.

Inventors: ORAM ROBERT KENNETH, ORAM, ROBERT, KENNETH
Applicants: BALMORAL GROUP, ORAM ROBERT KENNETH, BALMORAL GROUP LIMITED, ORAM, ROBERT, KENNETH
Application year: 1994
Main classification: B05D7
IPC codes: B05B13, B05D1, B05D7